The present invention pertains to a method and system for in situ spray fogging a mixture of hydrogen peroxide and alkali to reduce hydrogen sulfide concentrations in enclosed spaces, including gravity sewers and other structures in sewage collection systems.
Control of gaseous hydrogen sulfide and other gaseous sulfur compounds in sewage treatment systems, including gravity sewers, sewage pumping stations and other structures in sewage collection systems and treatment plants has been a long-standing problem. Relatively small diameter branch lines as well as large diameter trunk sewer lines and interceptors entering sewage treatment plants may extend substantial distances before a system collection and treatment station is available for treatment of foul air by conventional gas scrubber equipment and systems. Over such substantial distances odorous and toxic gases, such as hydrogen sulfide, may escape into the environment in proximity to a sewage system which can result in unhealthy, dangerous and clearly unpleasant circumstances for persons in the vicinity of such a system.
Moreover, the presence of toxic gases, such as hydrogen sulfide, in the vapor spaces of sewage conduits and in slimes which tend to accumulate on the conduit walls results in the formation of acids which contribute to significant corrosion of the conduits. Accordingly merely treating the liquid influent in a conduit does not result in treatment of acid substances which accumulate and are retained on the conduit walls and can cause significant corrosive action.
Furthermore, the expansion of municipal sewage collection and treatment systems as a consequence of residential and commercial development in a municipality or a change in the composition of sewage usually requires expansion of a central treatment facility including the addition of foul air treatment equipment such as conventional mist or packed-tower-type scrubbers. These devices are particularly capital intensive and require substantial maintenance effort and expense.
Still further, sewage collection and treatment systems which are subject to increased capacity requirements or systems which may over a period of time require handling of various concentrations of material which produce the noxious gases referenced hereinabove could benefit from localized control of foul air in the collection system and associated structures. The addition of air handling equipment and conventional scrubbers at such locations may be impractical and, of course, can require substantial expense. However, the present invention provides a method and system which overcomes, substantially, the aforementioned problems by utilizing the sewage handling structures themselves as foul air treatment or gas scrubber structures which provides significant advantages as will be appreciated by those skilled in the art.
The present invention provides a method of localized control of odor and corrosion in gravity sewers, sewage pumping stations and other structures in sewage collection systems and treatment plants by utilizing sewer conduits, plenums and similar structures for treatment of air-borne contaminants, such as hydrogen sulfide and other noxious and toxic gases, flowing through a sewage system and the like.
In accordance with one important aspect of the invention, a method is provided for injecting a dilute oxidizing liquid spray, mist or fog into the air space above flowing sewage in sewage structures, such as gravity sewers and the like, upstream of pumping stations or treatment plant headworks. The method contemplates providing a treatment injection point upstream of the area or structure where odor and/or corrosion control are required so that sufficient time is allowed for oxidation and/or adsorption of air-borne contaminants, including hydrogen sulfide and other reduced sulfur compounds.
In accordance with another aspect of the invention, a method of air-borne odor and corrosion control is provided in situ in sewer systems by injecting an alkali and peroxide solution through one or more atomizing or spray nozzles into a sewage conduit above the flowing influent and in quantities in proportion to the expected levels of toxic gases, such as hydrogen sulfide. The solution may be premixed and injected through a nozzle array into the foul air in the sewage system or the alkali and peroxide treatment components may be injected separately but in the vicinity of each other into the conduit. The method contemplates that the mist or fog is drawn along the sewage conduit by the flowing sewage and vapors in the vapor space of the conduit. Such vapor flow may be assisted by mechanical pumps or fans to draw the treated air and vapor mixture through a pump station or existing foul air scrubbing or treatment apparatus.
In accordance with still another aspect of the present invention, an improved method of corrosion control in sewage handling and treatment system is provided by injecting an oxidizing agent into sewage conduits at selected locations to oxidize air-borne hydrogen sulfide and other reduced sulfur compounds to prevent traversal of corrosive compounds through the entire sewage system and any treatment facilities connected thereto. The method contemplates the injection of a mixture of an oxidizing agent, such as hydrogen peroxide, and an alkali, such as sodium hydroxide. The use of an alkali is beneficial to assist the adsorption of the hydrogen sulfide into the spray/mist or fog, to accelerate the oxidation reaction and to neutralize the production of sulfuric acid from the reaction.
In accordance with yet another aspect of the invention, a method for odor control in sewage systems is provided wherein enclosed spaces in gravity sewers and similar structures are subject to the injection of a spray, mist or fog of diluted alkali, such as sodium hydroxide, at a point upstream of where odor control is required to temporarily neutralized the adverse effects of odorous substances, such as hydrogen sulfide, and in order to provide sufficient time for other injection agents to react with such contaminants in the enclosed spaces so as to permanently neutralize the adverse effects.
The present invention still further provides a system for injecting a spray or mist of an oxidizing agent and an adsorbing and ionizing agent for oxidizing toxic gases, such as hydrogen sulfide, and other sulfur compounds present in the air spaces of sewage handling and treatment systems and similar structure, which system may be placed permanently or temporarily at selected locations in sewage conduits, for example, upstream of a source of production of hydrogen sulfide and similar toxic gases. The system is adapted to mix and inject a dilute solution of hydrogen peroxide and sodium hydroxide as oxidizing and adsorption agents directly into a sewer pipe vapor space or plenum of a sewage handling structure to create intimate contact between the chemical spray or mist and the toxic vapors and contaminants in the vapor space. The system is capable of injecting a spray, mist or fog depending on the pressure and flow rates of the injected fluids.
In accordance with yet another aspect of the present invention, a system for injecting a spray, mist or fog of an oxidizing agent and an adsorption and ionizing agent into the air space of sewage handling and treatment structures is provided wherein a dilution water stream may be added to the oxidizing and alkaline adsorption agents prior to passing these agents through one or more atomizing or spray nozzles. Conversely, the oxidizing and adsorption agents may be added to a tank of dilution water from which a final solution is pumped through the spray nozzles. The system may be operated continuously when the concentration of the toxic contaminants, such as hydrogen sulfide, is great enough to warrant abatement thereof.
The system and method of the invention also provides the advantage that any of the adsorption and oxidizing agents, with or without dilution water, which are unreacted with airborne contaminants may be deposited on sewage conduit walls to neutralize corrosive substances deposited thereon and/or the agents merely fall into flowing liquid sewage in a sewage conduit or the bottom of a dry plenum or other structure. In this way unreacted agents will react with sulfides in the sewage influent resulting in further reduction of concentrations of toxic substances, such as hydrogen sulfide, and the adverse effects of same. Moreover, any unreacted oxidizing agent may provide dissolved oxygen to the sewage influent stream.
Those skilled in the art will further appreciate the above-mentioned features and advantages of the invention together with other superior aspects thereof upon reading the detailed description which follows in conjunction with the drawing.